MessageYour result file have an error: The order of your labels "SXZ" "SYZ" (and values) is bad, must be swapped to "SYZ" "SXZ",
as is explained in the GiD help (Postprocess data files):
" for Matrix results: six components (3D models)
3D: result_number_i Sxx_value Syy_value Szz_value Sxy_value Syz_value Sxz_value"
If you recalculate the roots of the matrix determinant polynomial, swapping this two values, then are obtained the GiD values of Si = 1.61E4, Sii = 1.13E4 and Siii = 4.26E3.
In fact, GiD not solve this cubic ecuation, because not only requires the eigenvalues, also requires the eigenvectors. It uses a Jacobi numerical method.
Regards
Enrique Escolano
----- Original Message -----
From: LEWIS, RANDEL E
To:
gidlist at gatxan.cimne.upc.es
Sent: Thursday, April 10, 2003 4:53 PM
Subject: [GiDlist] Principal stress components Si, Sii and Siii from Post Processor
I recieved confirmation from Miguel, in reply to my previous question (text copied at bottom of this email), that the Post Processor values Si, Sii and Siii are the principal stresses. However, I find the values calculated differ from those obtained from the roots of the matrix determinant polynomial S^3 - I1*S^2 + I2S - I3 = 0 where I1, I2 and I3 are the first, second and third invariants of the Cauchy stress tensor. The values I calculate (which agree with those from the program which generated the X, Y and Z average stress components shown below) are: S1 = 1.74E4, S2 = 7.55E3 and S3 = 6.68E3 as compared to GiD's values of Si = 1.61E4, Sii = 1.13E4 and Siii = 4.26E3.
How does GiD calculate these values?
Yes,
they are the main stresses of the tensor matrix.
given a matrix result, GiD calculates its eigen values and eigen vectors. Si, Sii, Siii are ordered by its eigen values. yes, sorry, the documentation is too brief about this question, we'll include an explanation about this in the documentation.
miguel
"LEWIS, RANDEL E" wrote:
The default Gid 7.1 Post Processor provides stress components Si, Sii
and Siii in addition to those obtained from the solid model
*flavia.res file. These are not defined in the supplied
documentation. Are they Principal Stresses derived from the X, Y and
Z stress components of the *.flavia.res file?
Randy
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